U.S. Pat. No. 4,709,737 discloses a barking device according to the preamble to claim 1 and a barking tool according to the preamble to claim 6. More specifically, this patent specification discloses a barking arm which at its outer end is formed with a concave seat surface and a barking tool with a convex mounting surface. Two main embodiments are shown, viz. a first embodiment in which the seat surface and the mounting surface have an essentially part-circular-cylindrical shape and a second embodiment in which the seat surface and the mounting surface are essentially part-spherical. By designing the seat surface and the mounting surface in this way, it is possible, by rotatingly displacing the barking tool in the seat surface of the barking arm, to locate the barking tool in different positions which provide different contact angles, and thus different degrees of aggressiveness, of the front barking-edge-forming edge portion to the circumferential surface of the log which is to be barked.
Such an embodiment is highly advantageous since different tree species may require different contact angles of the barking tools. Also when barking the same kind of tree species, the contact angle of the barking tool may have to be changed owing to a change in temperature, since, for instance, frozen bark is considerably more difficult to shear off than unfrozen bark.
Another common alternative is to manufacture barking tools which are made with different contact angles, allowing the barking tools to be changed when required, instead of changing the position of the barking tool on the barking arm. The drawback in this case, however, is that several sets of barking tools must be available for one and the same barking machine, and it is also time-consuming to completely exchange the barking tools, which in some cases may have to be done several times a day.
These drawbacks are eliminated by the embodiments that are disclosed in said U.S. Pat. No. 4,709,737. Among other things, one and the same set of barking tools can be mounted in two or more different mounting positions with different contact angles of the front barking-edge-forming edge portions to the circumferential surface of the log. However, there remain other problems and draw-backs.
According to a first embodiment as shown in FIGS. 1-4, the mounting surface and the seat surface are essentially part-circular-cylindrical. To lock the barking tool parallel to the axis of curvature of the part-circular-cylindrical surfaces, the mounting surface of the barking tool is made with a ridge and the seat surface of the barking arm is made with a groove perpendicular to the axis of curvature of the circular-cylindrical surfaces. In order to also lock the barking tool against motion in the longitudinal direction of the groove and the ridge, a turnable body is arranged in the barking arm, which body on the side facing the barking tool has an eccentrically positioned projection, which by turning of the body is settable in two different positions to engage in corresponding recesses in the mounting surface of the barking tool. In such a construction, the barking tool must be completely removed when reset since the body must be turned. Such a construction also comprises many separate parts and involves quite a number of machining steps of the barking tool as well as the barking arm.
In a second embodiment as shown in FIGS. 5-8, the mounting surface and the seat surface are part-spherical. The mounting surface of the barking tool has a ridge whereas the seat surface of the barking arm has three intersecting grooves. The ridge and the grooves lock the barking tool against motion essentially parallel to the intended direction of the feeding of the logs and the three intersecting grooves in the seat surface make it possible to mount the barking tool with its barking edge at three different angles relative to the direction of feeding of the logs in order to compensate for the tapered shape of the logs. In this construction however, the barking tool is not locked in the longitudinal direction of the ridge and the grooves, but these forces are fully absorbed by the shank of the screw with an increased risk of breaking the same. The spherical design also implies that the nut cooperating with the screw is not prevented from rotating, but can rotate as the screw is being tightened, which may make mounting difficult.
In a third embodiment as shown in FIGS. 9-12, the mounting surface and the seat surface are part-spherical like in the second embodiment. Locking of the barking tool both in the direction of feeding of the logs and perpendicular thereto is effected by means of small projections on the mounting surface of the barking tool, which projections can optionally engage in one of a plurality of recesses in the seat surface of the barking arm. Also in this case, the spherical design implies that there is no locking of the nut, but there is a risk of its rotating when tightening the screw. Furthermore, the projections and the recesses cause increased machining of the mounting surface and the seat surface, and there is a risk that the small recesses are blocked by dirt, resin and the like, which makes the resetting of the barking tool difficult.